This invention relates generally to improvements in fluid flow control systems and, more particularly, to a new and improved automatic, self-regulating, highly accurate drop flow control system for parenteral administration of medical fluids over a wide range of fluid flow rates and capable of utilizing a variety of different electromechanical output devices, such as positive pressure infusion pumps using stepping motors or the like, as well as controllers using electrically actuated I.V. tube pinchers.
The usual medical procedure for the gradual parenteral administration of liquids into the human body, such as liquid nutrients, blood or plasma, makes use of apparatus which is commonly referred to in the medical art as an intravenous administration set. The intravenous set usually comprises a bottle of liquid, normally supported in an inverted position, an intravenous feeding tube, typically of clear plastic, and a suitable valve mechanism, such as a roll clamp, which allows the liquid to drip out of the bottle at a selectively adjustable rate into a transparent drip chamber below the bottle. The drip chamber serves the dual function of allowing a nurse or other attendant to observe the rate at which the liquid drips out of the bottle and also creates a reservoir for the liquid at the lower end of the drip chamber to insure that no air enters the main feeding tube leading to the patient.
While observation of the rate of drop flow via the drip chamber is a simple way of controlling the amount of liquid fed to a patient over a period of time, its ultimate effectiveness requires that a relatively constant vigil be maintained on the drop flow, lest it cease entirely due to exhaustion of the liquid supply or become a continuous stream and perhaps increase the rate of liquid introduction to the patient to dangerous levels.
By way of example, it has been the general practice in hospitals to have nurses periodically monitor drop flow rate at each intravenous feeding or parenteral infusion station. Such monitoring of drop flow is a tedious and time consuming process, prone to error and associated, possible serious consequences, and resulting in a substantial reduction of the available time of qualified medical personnel for other important duties. Typically, the nurse monitoring drop flow rate will use a watch to time the number of drops flowing in an interval of one or more minutes, and she will then mentally perform the mathematics necessary to convert the observed data to an appropriate fluid flow rate, e.g., in cubic centimeters per hour or drops per minute. If the calculated flow rate is substantially different than the prescribed rate, the nurse must manually adjust the roll clamp for a new rate, count drops again, and recalculate to measure the new rate.
Obviously, each of the aforedescribed measurements and calculations and flow rate adjustments usually take several minutes time which, when multiplied by the number of stations being monitored and the number of times each station should be monitored per day, can result in a substantial percentage of total personnel time available. In addition, under the pressure of a heavy schedule, the observations and calculations performed by a harried nurse in measuring and adjusting flow rate may not always prove to be reliable and, hence, errors do occur resulting in undesired, possibly dangerous infusion flow rates.
In addition to the aforedescribed difficulties, the parenteral administration of medical liquids by gravity induced hydrostatic pressure infusion of the liquid from a bottle or other container suspended above a patient, is very susceptible to fluid flow rate variation due to changes in the liquid level in the bottle, changes in temperature, changes in the venous or arterial pressure of the patient, patient movement, and drift in the effective setting of the roll clamp or other valve mechanism pinching the feeding tube. Moreover, there are a number of situations, such as in intensive care, cardiac and pediatric patients, or where rather potent drugs are being administered, where the desired drop flow rate must be capable of precise selection and must not drift beyond certain prescribed limits. In addition, it is extremely important in such situations for medical personnel to be informed of undesired fluctuations in flow rate, failure of the fluid delivery system, or exhaustion of liquid supply when the bottle is emptied.
It will be apparent, therefore, that some of the most critical problems confronting hospital personnel faced with an overwhelming duty schedule and limited time availability are the problems of quickly, easily, reliably and accurately monitoring and regulating drop flow rate in the parenteral administration of medical liquids.
In recent years, a number of electrical monitoring systems, drop flow controllers and infusion pumps have been developed to accomplish the various tasks of sensing and regulating drop flow rates. Some of these devices have also been capable of activating alarms when a potentially dangerous condition exists, thus freeing medical personnel to some extent for other duties. However, while such monitoring and drop rate control devices have generally served their purpose, they have not always proven entirely satisfactory from the standpoint of cost, complexity, stability, reliability, accuracy, adaptability to different types of electromechanical output devices, or precision of adjustment over a wide range of selected flow rates. In addition, such systems have sometimes been subject to drift and substantial flow rate variations due to changes in temperature, feeding tube crimps, variations in venous or arterial pressure of the patient, or variations in the height of the bottle or solution level within the bottle. Substantial difficulties have been experienced particularly in connection with establishing and maintaining such accurate drop flow at very low flow rates.
Hence, those concerned with the development and use of parenteral fluid administration systems, and particularly those concerned with the design of automatic fluid flow control systems, have long recognized the need for improved, relatively simple, economical, adaptable, reliable, stable and accurate devices for fluid flow control which obviates the aforedescribed difficulties. The present invention clearly fulfills this need.